Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965772AbbD1MJF (ORCPT ); Tue, 28 Apr 2015 08:09:05 -0400 Received: from mx1.redhat.com ([209.132.183.28]:58338 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965419AbbD1MJC (ORCPT ); Tue, 28 Apr 2015 08:09:02 -0400 Date: Tue, 28 Apr 2015 07:08:38 -0500 From: Josh Poimboeuf To: Jiri Kosina Cc: x86@kernel.org, Borislav Petkov , Kees Cook , Seth Jennings , Vojtech Pavlik , linux-kernel@vger.kernel.org, live-patching@vger.kernel.org Subject: Re: [PATCH 1/2] x86: introduce kaslr_offset() Message-ID: <20150428120838.GA16487@treble.redhat.com> References: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23.1-rc1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2220 Lines: 62 On Mon, Apr 27, 2015 at 04:28:07PM +0200, Jiri Kosina wrote: > Offset that has been chosen for kaslr during kernel decompression can be > easily computed as a difference between _text and __START_KERNEL. We are > already making use of this in dump_kernel_offset() notifier. > > Introduce kaslr_offset() that makes this computation instead of > hard-coding it, so that other kernel code (such as live patching) can make > use of it. > > Signed-off-by: Jiri Kosina > --- > arch/x86/include/asm/setup.h | 6 ++++++ > arch/x86/kernel/setup.c | 2 +- > 2 files changed, 7 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/include/asm/setup.h b/arch/x86/include/asm/setup.h > index f69e06b..785ac2f 100644 > --- a/arch/x86/include/asm/setup.h > +++ b/arch/x86/include/asm/setup.h > @@ -65,12 +65,18 @@ static inline void x86_ce4100_early_setup(void) { } > * This is set up by the setup-routine at boot-time > */ > extern struct boot_params boot_params; > +extern char _text[]; > > static inline bool kaslr_enabled(void) > { > return !!(boot_params.hdr.loadflags & KASLR_FLAG); > } > > +static inline unsigned long kaslr_offset(void) > +{ > + return (unsigned long)&_text - __START_KERNEL; > +} > + > /* > * Do NOT EVER look at the BIOS memory size location. > * It does not work on many machines. > diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c > index d74ac33..5056d3c 100644 > --- a/arch/x86/kernel/setup.c > +++ b/arch/x86/kernel/setup.c > @@ -834,7 +834,7 @@ dump_kernel_offset(struct notifier_block *self, unsigned long v, void *p) > { > if (kaslr_enabled()) { > pr_emerg("Kernel Offset: 0x%lx from 0x%lx (relocation range: 0x%lx-0x%lx)\n", > - (unsigned long)&_text - __START_KERNEL, > + kaslr_offset(), > __START_KERNEL, > __START_KERNEL_map, > MODULES_VADDR-1); It looks like kaslr_offset() can also be used by arch_crash_save_vmcoreinfo() in machine_kexec_64.c. -- Josh -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/